Sound recording system



FIP8212 XR Aug. 1 1932- I T.'R. GOLDSBOROUGH SOUND RECORDING SYSTEM Filed May 1, 1930 EXAMINER 1,"; X 1' HE -v 9:5 if:fl'2.'i-ill' zzfi L .e-f ml; n. :w" ,e r J. .1 'm: i i T o f p UNITED, STATES ,RATENT, :OFFICE, 1 "I ii .2 1 izi il -hip"! L 4 5 60; =17 I .1'5 I giante s s'ssmssonomaas assrsnon ago g a: L,, .I NGHOUSE IELECTRIC a; macrunmc corarm, a oonronarrou or rnnn-*- Y" KI BO P Q P HQS S E '1 a puaiioameajrayi, 19:6, saris; in, 442,873. A I y if "1' 1m". -L. "1 z r, 4 i a Irv. i \i My invention relatesto photo-acoustlcreftrol-of the recording amphfier in such man- 'corders and has particular relation to photornenthat thel'end of the beam does not pass .heou stic optical used in producing Pbeyond a black line-drawn on the surface.-

sound records of the variable-width This method'of regulating the magnitude w, A hoto-acou'stic o tical I stemf this -of'the deflection of the recordin 1i ht beam P..Y s. natureordinarilyacomprises aisourceofihght, 1s, obviously, extremely crude, and, the dilfi- :vmas'k and a system of lenses for condensing cul'tles that arise in its use are numerous; -the light; A mirror, mounted on the moving .gItis virtually impfossibleafor the operator -element of a galvanometer, is illuminated by stov accurately ahgn the end of the light-beam the'condensed light, and a'beam, substanthe black line, .and,,consequ y,- he i atially rectangular intransvers'e cross section, obliged to hold the volume'to sucha magniisreflected firom the mirror. Ani-lluminated --tude that there'iis a'space'between the end wrectangle is thus produced-on ;an.obstruc- :of the recording light beam andthegline. .tion interposed in the path-of the light beam Furthermore; sudden variations-in volume a and,when the mirror. ss-oscillated by reason -'tak,eiplace: before-the. operator can prepare jp f the motion of its mounting Qunder theacfor, them Eand,-as ajresult,'the zpeaksvo'f the action of the energized gal-vanometer' magnet, -soui1d track, whe re short, loud sounds are in- .fth'e position of therectangle on the obstrucinterposed between .long,'soft ones almost tion is changed. anvanably-cut ofil, Such aisituation results Y E-The light beam reflected from the galan aicom'plete destruction czvanometermirror is attenuated and partially 1n recorded music. Y a 1 illuminates a ,slit which is, in turn,'--. imaged In recording-sound by the photo-acoustic on the'film; A method,-it:has been customarytouseanum- The variation in {the audimcurrent proz-ber oflrecorders and thus: to make certain 25 @duces' variations .the'amplitude' :of the "that, at least, one negative, which is tolerably oscillations of the galvanometermirror, and undistorted, will be available in the- .end. {consequent variations in the length of the slit :zFilID- isvrrather' expensive and, consequently, illuminated. The variahle-width-slit image rsuch -pr0c'essis, rather -costly.. Moreover, g:isfimpressed in germanent form on the where only a single recorder isvavailable, -Excessiede e L ,efieoted by -excess ive gcurrent in the rgalvareason of improper monitoring, 'and the contno meter, gvvhich is known-as Sover-shooting, sequent necessity of recording again, involvjes ,sproduces distortionin'the photo acousticrec-am. considerable-expense.

ord' that appears as distortions in the sound It is, accordingly, an object-of my 'inv'eni .reproduced' from the record. I Sinceithetotah l l Y F iiOL in Position of th eam -;tem-for a photo-acoustic sound-recorder. r, is ordinarily as nall veryl littlegover-shooting Another object of my inventionlis topr'oj is sufi icient to ,distort t e, wave recorded on 1' vide a recording optical systemequipped-wvith the M H means for immediately and clearly signaling as; so undcon-wanoperator that; the recording lightbeam,

u ge of the, pr or 1a,1 :t, v with which ;I am f a--1v;;= An additional objectof my-invention' is-lto 54 1 1 3 t eg-mon topugssy tem, tha ls-gpro- 2 provide a 'photo aco'ustic optical system gvided iorypreventing over shooti ng, ,is not equippedwith.amoliitoring devic'ethat. shall a :2 24,52 at s to y r g i yj reflecting surface is provided in the pathofggproduce-a signal indicating-.-that1said flight beamhes b ex r yv efle ed-a; variafi n, in p i ti nis t 1'st ll-pnc he o iectot yamvq tionzi 3G J h I- sem this r weispb rve ':p ide a 'fphefiwac us ei ecgrden (stem smut brassy .7 mvh gu ates-t e g i i:c01 --irhem !;fiha em iaeeet lefl en metlee lye f is f i a p g j V ap a V i a to x F- i ction :Of the light; beam, the production 'ofthe' distorted negative, by

:tion to produceen efiective monitoringfsys-v;

diffuse she actuated by :the recording: light,- beami A still further object of my invention is to provide a photo-acoustic recording system wherein the magnitude of the deflection of the light beam is regulated automatically by the light beam itself.

More specifically rstatedfit is an Yibjecv'df my invention toprovide, for a photo acousti'c recording system, a photo-sensitive-si ling device that shall respondte therecordmagnitude of the deflection o f said light' beam- 3' I a According to my invention, I provide a recording optical system. equipped fil hffiai mirror that reflects the over-shot light of the recording light beam intoone or a plurality of photo-sensitive devices. The latte'r,"in turn, when energized, actuate an electrical relay system to produce a signal, thus notifying the operator that the system is overshooting. T

In a modification of my'invention, I so couple the-output of the relay system to'the recording amplifier that the deflection of the recording light beam is automatically regulated from the photosensitive means. I

The novel features that I consider characteristic of my invention are set forth with particularity in the appended claims. The invention itself, however, both-asto its organization and its method of operation, together with additional objects and advantages thereof, will best be understood from the following description of specific embed-L 2 ments when read in connection with the ac companying drawing, in which,

Figure 1 is a schematic drawin showing a photo-acoustic recording optica system; Fig. 2 is a view, in front elevation, of a film 1:trip showing a properly recorded sound trac I m re it] ,Fig. 3 is a view, in front elevation,-of a film strip showing a sound track thathas been over-shot; V m Fig. 4 is a schematic drawin showing the principal features of an embodiment of my invention; '1

Fi 5 is a sectional view-taken along line V-ofFigfi; 1 .-z 1:. 'f i Fig. 6 isa view,in section, showing'the actual disposition of the elements constitut ing my invention, and, j a

' ig. 7 is a schematic drawing, showing a modification of my invention. f I -;1... The apparatusshown in Fig. 1 comprises a source of illumination 1,:the rays from which traverse a rectangular mask 3 and are converged, by a condensing lens 5, to 'illuminate a mirror 7 that is rigidly mo'unted'on the moving element of a recording galvanometer (not shown). {The light 'reflected from the galvanometer mirror 7 isconverged; bya cylindrical lens 9 to produce an elongated rectangulaiimage for illuminating a portion of aislit 11. As the suspension bf-the galvanomwas ntrnnmur.

eter is motivated by the current from the recording amplifier, the galvanometer mirror 7 oscillates to cause the rectangular image on the slit 11 to move longitudinally along the slit and illuminate the section of the slit that isZdafi k When the galvaiiomet'e'r is not excited by the andio current.

gnal----- Theratio of the fraction of the slit 11 that L A firilluminated when there is zero current .in mg light beam to efiecta reduction intli rltliefgalvanoineter, to; the total length of slit, determines the magnitude of the modulation cfthe soundtrack, i. e. the maiiim'um volume of sound reproducable from a sound track undeiggivenconditions; For 100% modulation, the slit is completely dark or completely illuminated'depending on -the polarity of the modulation. That is to say, if the modulation is positive, the whole slit is illuminated and, if it is negative, the whole slit is dark.

*An image of the slit 11 is cast on a moving film strip 13by an objective 15 and, since illumination of a certain length of slit produces a slit image on the film 13-of proportionate length, a photographic strip 17 is produced'on the film that has a width which varies in accordance with the response of the gal-vanome'ter mirror to the audio-current.

wou d It is seen that, if thegalvanometer' mirror is excessively deflected, 'the extreme end of the "illuminated rectangle is obstructed by the boundaries-of the slit and, consequently, the peaks of the sound track are flat,-as shown in Fig. '3,rather than round, as shown in Fig in accordance with my invention, Iprov'ide a reflector 19 adjacent to the slit 11 and at an angle to the plane thereof; When'the recording light beam is excessively-deflected, the mirror 19 reflects the light into one or a plurality of photo-sensitive cells 21. The cells 21 may be coupled to an amplifier 23 or they maybe connected in a. circuitin-such manner as to actuate a grid-glow tube or a similar relay. 'In"any-case, a meter 24, disposed in the output circuit of the device 23 and actuated'by the photo-cell 21, responds, when the photocell is energized to notify an operator th'at'therecording light beam is being ex cessively deflecte T In Figs.'5 and 6,the' actual disposition of the apparatus provided according to my invention is shown. The slit 11 is mounted in a hollow tube 25, one end of which is adapted to receive the objective 15. Supported on a bracket27' of transverse V-section, adjacent tothe bounding edge of the slit 11, is the mirror 19. The photo-electric cell 2l'is sup: ported an in'cl'osure 29 which is fastened to'the tube25nea'r'a'n opening therein and is capable of receiving the light reflected from themirror19. I 1 j Although, in the preferredembodiment of my invention shown herein, the mirror'19 is disposed adjacent w the slit 11, it is apparent that the mirror maybe located'in any one of numerous other positions in the system where it is capable of responding to over-shooting.

As has been explained hereinabove, in photo-acoustic optical systems, constructed according to the teaching of the prior art, the movement of the light beam, on a highly diffuse reflecting surface equipped with a black line, is observed. It is possible to locate the monitorin mirror adjacent to the line on the surface. ecording optical systems wherein the monitoring mirror 19 is disposed in other positions than at the slit 11 are within the scope of my invention.

In Fig. 7, a modification of my invention is shown wherein the photo-cell 21 is so disposed that it automatically regulates the magnitude of amplification of the recording amplifier. The outut of an amplifier or relay 23, actuated by the photo-cell 21, supplies a grid-biasing voltage to the tube 31 of the voice-amplifier in such direction that the amplification is decreased when the current in the monitoring photo-cell 21 is increased.

As shown in Fig. 7 the amplifier 23 is connected in the circuit of the amplifying stage that is directly coupled to the microphone 33. To prevent the system from being excessively affected by a sudden rush of current from the amplifier 23, a condenser 35 is connected in parallel with the resistor 37 across which the valve voltage is impressed.

The single-stage amplifier is also shown as directly coupled to the galvanometer 39. It is, of course, within the scope of my invention to apply the device to a system wherein a plurality of stages of amplification are present and to couple the valve 23 to any one or to any number of these stages.

My invention has particular application to sound-reproducing equipments, such as public-address systems. It may be used to limit the volume of the output of such apparatus. The electrical circuit for such system is also illustrated schematically in Fig. 7. A galvanometer 39, similar to the ordinary recording galvanometer, is connected in parallel with the loud speaker 41, in the output of the amplifying system. The vibrating mirror 42 of the galvanometer determines the magnitude of deflection of a light beam that is adapted to energize the photo-cell 21, if deflected beyond a predetermined angle. The photo-cell 21 is energized by a beam from a source 43 which is projected thereon when the galvanometer mirror 42 is excessively deflected. The photo-cell 21, in turn, actuates the amplifier 23 which automatically regulates the amplification, as has been explained hereinabove.

Although I have shown and described certain specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as may be necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In combination with means for transforming sound vibrations into vibratory electric currents, a galvanometer of the mirrortype traversed by said currents, a light source adapted to project a light-beam incident upon said galvanometer mirror, an o tical slit through which the reflected beam om said galvanometer mirror is projected, an edge of said reflected beam crossing said slit in the mid-portion thereof when no current flows in said galvanometer and moving back and forth toward the ends of said slot when current vibrations flow therein, a reflector p0- sitioned beyond one end of said slit and positioned to reflect said reflected beam only when its edge overruns the end of said slit, a photo-electric device positioned to be struck by the beam emanating from said reflector, and signal means connected to respond to the excitation of said photo-electric device.

2. In combination with means for causing a light-beam to oscillate in correspondence with sound vibrations, a light-sensitive re ceiving device onto which said light-beam is projected through an optical slit, a mirror adjacent said slit positioned to be struck by said beam only when, in its oscillations, it overruns a margin of said slit, a photo-electric device positioned in the path of the beam when reflected from said mirror, and a signal device connected to respond to the excitation of said photo-electric device.

In testimony whereof, I have hereunto subscribed my name this 24th day of April, 1930.

THADDEUS R. GOLDSBOROUGH. 

